1. Field of the Invention
The present invention relates to a system for transmitting an optical signal over an optical waveguide containing a fiber-optic amplifier.
2. Description of the Prior Art
A system for transmitting a first optical signal over an optical waveguide containing a fiber-optic amplifier which includes an amplifying length of fiber, a pump source, and a wavelength-selective fiber-optic coupler for coupling the pump source to the amplifying length of fiber is known from "EOCC '89", Fifteenth European Conference on Optical Communication, Sept. 10-14, 1989, Gothenburg, Sweden, Proceedings, Vol. 1, Regular Papers, TuA 5-7, pages 86 to 89.
In the above-referenced article, two different system configurations are explained. In the first ("co-propagating configuration"), the light from the pump source is launched into the Er.sup.3+ -doped length of fiber via a coupler which is located in front of the amplifying length of fiber when viewed in the direction of transmission of the optical signal to be amplified. In the second system configuration ("counter-propagating configuration"), the coupler is located behind the length of fiber when viewed in the direction of transmission of the signal to be amplified. Sometimes it is desirable or necessary in transmission systems to transmit, in addition to the first optical signal, a second optical signal from the location of the fiber-optic amplifier in one direction or the other.